Where Are Ethereum Smart Contract Code and Data Stored?

Ethereum Architecture Overview

Ethereum's blockchain structure consists of several key components:

1. Version Number
2. Previous Block Hash
3. Timestamp
4. Nonce
5. Target Hash
6. MPT (Merkle Patricia Trie) - Three Core Trees

Transaction Tree

• Contains all transactions at the base layer

State Tree

• Manages accounts

  • Regular accounts (with storage space only)
  • Contract accounts (with both storage space and executable code)

Receipt Tree

• Stores transaction receipts
• Designed for efficient SPV (Simplified Payment Verification) indexing

The tree structures themselves store key-value pairs as hash references. When a smart contract is deployed:

• A new contract account is created
• Contains compiled bytecode (for EVM execution)
• Includes dedicated storage space for data persistence
• Requires ABI (Application Binary Interface) for interaction

Understanding Ethereum Smart Contracts

1. What Are Smart Contracts?

Self-executing programmatic agreements with:

• Predefined methods
• Variable states
• Written primarily in Solidity (JavaScript-like syntax)

2. Execution Triggers

Two execution modes:

• State-changing operations: Require transactions (gas fees apply)
• Read-only operations: Local calls (no gas fees)

3. Execution Environment

Requirements for execution:

• Ethereum client with EVM (Ethereum Virtual Machine)
• Contract address (for identification)
• ABI (for method accessibility)

4. Current Limitations

Smart contracts cannot:

• Access external web resources
• Perform complex file operations
• Execute unrestricted computations

Storage Mechanisms Explained

Smart Contract Code Storage

• Persisted permanently on blockchain
• Stored via codeHash in account state
• Deployed through transaction inclusion in blocks
• Accessible via contract address

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Data Storage Principles

Key characteristics:

1. Each contract maintains dedicated storage (key-value database)
2. Public variables accessible via getter methods
3. All data persists in blockchain's underlying database
4. Historical modifications may be pruned over time

Contract Self-Destruction Mechanism

• Invoked via selfdestruct(recipient)
• Removes contract from state tree (not historical blocks)
• Transfers remaining ETH to recipient
• Does not physically delete code from blockchain

Practical Considerations

Locating Historical Contracts

• Address-based lookup system
• State tree maintains current references
• Historical blocks remain immutable

Storage Efficiency Factors

• Regular accounts: Minimal storage
• Contract accounts: Code + persistent storage
• Merkle tree structure enables efficient verification

FAQ Section

Q: Can deleted smart contracts be recovered?

A: No - once self-destructed, contracts become inaccessible, though their historical existence remains verifiable.

Q: How much does smart contract storage cost?

A: Storage operations consume gas proportional to data size and complexity.

Q: Where can I view public contract variables?

A: Through wallet interfaces using contract addresses and ABI information.

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Q: Why can't smart contracts access web APIs?

A: EVM design prioritizes deterministic execution, excluding external dependencies that could cause consensus failures.

Q: How long does contract data persist?

A: Indefinitely - blockchain's immutable nature ensures permanent availability unless explicitly pruned.

Q: What happens to contract storage after destruction?

A: Storage space becomes inaccessible but remains physically present in historical blocks.